1  /* s_scalbnl.c -- long double version of s_scalbn.c.
       2   */
       3  
       4  /* @(#)s_scalbn.c 5.1 93/09/24 */
       5  /*
       6   * ====================================================
       7   * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
       8   *
       9   * Developed at SunPro, a Sun Microsystems, Inc. business.
      10   * Permission to use, copy, modify, and distribute this
      11   * software is freely granted, provided that this notice
      12   * is preserved.
      13   * ====================================================
      14   */
      15  
      16  #if defined(LIBM_SCCS) && !defined(lint)
      17  static char rcsid[] = "$NetBSD: $";
      18  #endif
      19  
      20  /*
      21   * scalbnl (long double x, int n)
      22   * scalbnl(x,n) returns x* 2**n  computed by  exponent
      23   * manipulation rather than by actually performing an
      24   * exponentiation or a multiplication.
      25   */
      26  
      27  #include <math.h>
      28  #include <math_private.h>
      29  #include <math_ldbl_opt.h>
      30  
      31  static const long double
      32  twolm54 = 5.55111512312578270212e-17, /* 0x3C90000000000000, 0 */
      33  huge   = 1.0E+300L,
      34  tiny   = 1.0E-300L;
      35  static const double
      36  two54 = 1.80143985094819840000e+16, /* 0x4350000000000000 */
      37  twom54 = 5.55111512312578270212e-17; /* 0x3C90000000000000 */
      38  
      39  long double __scalbnl (long double x, int n)
      40  {
      41  	int64_t k,l,hx,lx;
      42  	union { int64_t i; double d; } u;
      43  	double xhi, xlo;
      44  
      45  	ldbl_unpack (x, &xhi, &xlo);
      46  	EXTRACT_WORDS64 (hx, xhi);
      47  	EXTRACT_WORDS64 (lx, xlo);
      48  	k = (hx>>52)&0x7ff;		/* extract exponent */
      49  	l = (lx>>52)&0x7ff;
      50  	if (k==0) {				/* 0 or subnormal x */
      51  	    if ((hx&0x7fffffffffffffffULL)==0) return x; /* +-0 */
      52  	    u.i = hx;
      53  	    u.d *= two54;
      54  	    hx = u.i;
      55  	    k = ((hx>>52)&0x7ff) - 54;
      56  	}
      57  	else if (k==0x7ff) return x+x;		/* NaN or Inf */
      58  	if (n< -50000) return tiny*copysignl(tiny,x); /*underflow */
      59  	if (n> 50000 || k+n > 0x7fe)
      60  	  return huge*copysignl(huge,x); /* overflow */
      61  	/* Now k and n are bounded we know that k = k+n does not
      62  	   overflow.  */
      63  	k = k+n;
      64  	if (k > 0) {				/* normal result */
      65  	    hx = (hx&0x800fffffffffffffULL)|(k<<52);
      66  	    if ((lx & 0x7fffffffffffffffULL) == 0) { /* low part +-0 */
      67  		INSERT_WORDS64 (xhi, hx);
      68  		INSERT_WORDS64 (xlo, lx);
      69  		x = ldbl_pack (xhi, xlo);
      70  		return x;
      71  	    }
      72  	    if (l == 0) { /* low part subnormal */
      73  		u.i = lx;
      74  		u.d *= two54;
      75  		lx = u.i;
      76  		l = ((lx>>52)&0x7ff) - 54;
      77  	    }
      78  	    l = l + n;
      79  	    if (l > 0)
      80  		lx = (lx&0x800fffffffffffffULL)|(l<<52);
      81  	    else if (l <= -54)
      82  		lx = (lx&0x8000000000000000ULL);
      83  	    else {
      84  		l += 54;
      85  		u.i = (lx&0x800fffffffffffffULL)|(l<<52);
      86  		u.d *= twom54;
      87  		lx = u.i;
      88  	    }
      89  	    INSERT_WORDS64 (xhi, hx);
      90  	    INSERT_WORDS64 (xlo, lx);
      91  	    x = ldbl_pack (xhi, xlo);
      92  	    return x;
      93  	}
      94  	if (k <= -54)
      95  	  return tiny*copysignl(tiny,x); 	/*underflow*/
      96  	k += 54;				/* subnormal result */
      97  	lx &= 0x8000000000000000ULL;
      98  	hx &= 0x800fffffffffffffULL;
      99  	INSERT_WORDS64 (xhi, hx|(k<<52));
     100  	INSERT_WORDS64 (xlo, lx);
     101  	x = ldbl_pack (xhi, xlo);
     102  	return x*twolm54;
     103  }